feat(lis2mdl): Add OLED digital compass example.

Author: Kaan Ozen

lib/lis2mdl/README.md

@@ -213,6 +213,7 @@ print("Register dump:", regs)
 | `power_on()` / `power_off()`      | Power management               |
 | `soft_reset()` / `reboot()`        | Sensor reset functions         |
 
+
 ---
 
 ## Examples
@@ -229,6 +230,7 @@ print("Register dump:", regs)
 | low_power_one_shot.py       | Energy-efficient sampling example. Uses `power_off()` between readings and `read_one_shot()` every 10 seconds, then prints values and free memory. |
 | magnet_compass.py           | Flat compass example that computes heading and cardinal direction from the LIS2MDL magnetic field. Useful for basic orientation demos. |
 | magnet_fieldForce.py        | Magnetic field magnitude example that shows total field strength in microtesla. Useful for observing magnetic disturbances and relative field changes. |
+| compass_display.py | Graphical compass with OLED display |
 
 ---
 

lib/lis2mdl/examples/compass_display.py

@@ -0,0 +1,136 @@
+"""Digital compass example using LIS2MDL and SSD1327 OLED.
+
+Reads the magnetic heading using the built-in flat heading method,
+and draws a dynamic compass needle on the display using lines.
+Includes a preliminary calibration step.
+"""
+
+from math import cos, pi, sin
+from time import sleep_ms
+
+import ssd1327
+from lis2mdl import LIS2MDL
+from machine import I2C, SPI, Pin
+
+# Layout Constants for Round Screen
+CENTER_X = 64
+CENTER_Y = 54
+COMPASS_RADIUS = 42     # Radius for the outer border of the compass
+NEEDLE_LENGTH = 35
+
+TEXT_HEAD_X = 36
+TEXT_HEAD_Y = 100
+TEXT_DIR_X = 36
+TEXT_DIR_Y = 112
+
+CARD_N_X = 60
+CARD_N_Y = 16
+CARD_S_X = 60
+CARD_S_Y = 84
+CARD_E_X = 96
+CARD_E_Y = 50
+CARD_W_X = 24
+CARD_W_Y = 50
+
+CALIB_MSG1_X = 12
+CALIB_MSG1_Y = 50
+CALIB_MSG2_X = 4
+CALIB_MSG2_Y = 70
+
+def draw_circle(fbuf, x0, y0, r, c):
+    """Draw a circle using the integer midpoint circle algorithm."""
+    f = 1 - r
+    ddf_x = 1
+    ddf_y = -2 * r
+    x = 0
+    y = r
+
+    fbuf.pixel(x0, y0 + r, c)
+    fbuf.pixel(x0, y0 - r, c)
+    fbuf.pixel(x0 + r, y0, c)
+    fbuf.pixel(x0 - r, y0, c)
+
+    while x < y:
+        if f >= 0:
+            y -= 1
+            ddf_y += 2
+            f += ddf_y
+        x += 1
+        ddf_x += 2
+        f += ddf_x
+
+        fbuf.pixel(x0 + x, y0 + y, c)
+        fbuf.pixel(x0 - x, y0 + y, c)
+        fbuf.pixel(x0 + x, y0 - y, c)
+        fbuf.pixel(x0 - x, y0 - y, c)
+        fbuf.pixel(x0 + y, y0 + x, c)
+        fbuf.pixel(x0 - y, y0 + x, c)
+        fbuf.pixel(x0 + y, y0 - x, c)
+        fbuf.pixel(x0 - y, y0 - x, c)
+
+# Hardware Initialization
+i2c = I2C(1)
+mag = LIS2MDL(i2c)
+
+spi = SPI(1)
+dc = Pin("DATA_COMMAND_DISPLAY")
+res = Pin("RST_DISPLAY")
+cs = Pin("CS_DISPLAY")
+display = ssd1327.WS_OLED_128X128_SPI(spi, dc, res, cs)
+
+try:
+    # Calibration Phase
+    display.fill(0)
+    display.text("Calibrating...", CALIB_MSG1_X, CALIB_MSG1_Y, 15)
+    display.text("Move in 8-shape", CALIB_MSG2_X, CALIB_MSG2_Y, 15)
+    display.show()
+    sleep_ms(100)
+
+    print("Calibrate the magnetometer by moving it in a figure-eight pattern.")
+    mag.calibrate_minmax_3d()
+    print("Calibration complete.")
+
+    # Main Compass Loop
+    while True:
+        heading_deg = mag.heading_flat_only()
+        direction = mag.direction_label(heading_deg)
+
+        # Convert to radians for the trigonometric functions
+        # 0 degrees is North (Up), 90 is East (Right)
+        heading_rad = heading_deg * pi / 180.0
+
+        # Calculate the end coordinates of the compass needle
+        end_x = CENTER_X + int(NEEDLE_LENGTH * sin(heading_rad))
+        end_y = CENTER_Y - int(NEEDLE_LENGTH * cos(heading_rad))
+
+        # Drawing Phase
+        display.fill(0)
+
+        # Draw the compass outer border (circle)
+        draw_circle(display.framebuf, CENTER_X, CENTER_Y, COMPASS_RADIUS, 15)
+
+        # Draw Cardinal Points (N, E, S, W)
+        display.text("N", CARD_N_X, CARD_N_Y, 15)
+        display.text("S", CARD_S_X, CARD_S_Y, 15)
+        display.text("E", CARD_E_X, CARD_E_Y, 15)
+        display.text("W", CARD_W_X, CARD_W_Y, 15)
+
+        # Draw the center dot and the needle
+        display.framebuf.fill_rect(CENTER_X - 1, CENTER_Y - 1, 3, 3, 15)
+        display.framebuf.line(CENTER_X, CENTER_Y, end_x, end_y, 15)
+
+        # Display the heading text and direction label at the bottom
+        display.text("{} deg".format(int(heading_deg)), TEXT_HEAD_X, TEXT_HEAD_Y, 15)
+        display.text("Dir: {}".format(direction), TEXT_DIR_X, TEXT_DIR_Y, 15)
+
+        display.show()
+        sleep_ms(50)
+
+except KeyboardInterrupt:
+    pass
+finally:
+    # Clean up and power off display on exit
+    display.fill(0)
+    display.show()
+    sleep_ms(100)
+    display.power_off()